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Since jet fuel is cheaper, why do pistons still use av-gas?
Since jet fuel is cheaper, why do pistons still use av-gas? Why is 100LL used at all?

Similar to https://aviation.stackexchange.com/questions/3513/why-dont-small-planes-use-turbine-turboprop-engines

First off, there are some light aircraft powered by diesel like the Piper Archer DX and the Diamond DA42. It should be noted both come in a 100LL powered version as well. As it stands now the FAA is looking for a replacement for 100LL but has not yet decided/found one. There are also some airplanes out there that can run on mogas. But anyway, more to the point, you cant simply put diesel into a regular engine as the ignition system and compression requirements are different. Thus to convert a plane to diesel you need a different engine all together. With that in mind most certifying bodies dont just let you swap airplane engines to any engine you see fit. The engine would need to be certified for the air frame which is a costly proposition. Thus it is sensible and economical to keep the current engines running. There are some efforts like those made by piper and diamond to slowly make diesel aircraft available.
As to why 100LL is used, this stems mostly from history. The vast majority of the general aviation fleet both physically and simply in design, stems from the dawn of the jet age. When the lines for the 172 were first drawn there was plenty of 100LL to go around, it was for lack of a better term, the logical choice.

Although even if a plane can run on mogas and I'm sure they sell it somewhere, I've never really seen it sold at most small airports.

TL:DR: Jet-A is cheaper than 100LL, but the support systems and availability are not yet in place to make engines that burn Jet-A an economical choice for private owners looking to retrofit their existing airplanes in the US.
Long Answer
While the fuel type may be cheaper, the cost of retrofitting an airplane with a diesel burning engine is not. With the price delta between AvGas and Jet-A, it takes a (reasonably) long time (if you're not a flight school or active club) to recoup the cost of the engine retrofit.
There are some additional considerations, such as the chicken-and-egg scenario that small airports often only stock 100LL, limiting where you can fly (if you hope to fill up on arrival).
It's frustratingly difficult to find current new prices (everyone wants you to "call for price"), but the ones I could find show a $116,000 difference between the Jet-A burning Skylane and the 100LL one (2013 and 2012 prices, respectively).
Skylane JT-A base price \$515,000
Skylane T182 base price \$398,100

So it would still take a while, even with a new plane to recoup the additional cost.

André Teissier-duCros, a former SMA consultant...published an analysis in August [2014] comparing various flight school business scenarios. Teissier-duCros calculated
  (assuming a price break of 59 cents per gallon on Jet A compared to
  avgas, and a two-year replacement cycle, among other things) that a
  used gasoline-powered Cessna 172 or 152 would break even at 150 hours,
  while a Cessna 172 Jet-A conversion (from either Premier Aircraft
  Sales of Florida or Redbird/RedHawk in Texas) would require 325 hours
  to break even. Beyond 600 hours, aircraft burning Jet A begin to
  generate more net profit for the operator than avgas alternatives...

Outside the US, however, AvGas is extremely expensive and can be hard to come by, so their is definitely a greater demand for these types of engines in airplanes outside of the US.
A Flying Magazine article from 2013 offers this explanation as to why our diesel future is still a ways away:

Still, no matter how good the technology becomes, diesels won’t
  supplant gasoline engines in America anytime soon. One reason is the
  sheer number of gasoline piston engines out there, flying in
  everything from aging Cessna 150s to brand new Cirrus SR22s — around
  225,000 of them in all. Another is the continuing dominance of
  gasoline engines in nearly every production piston single and twin
  sold today. And many smaller general aviation airports throughout the
  United States sell only 100LL avgas, limiting where you can fly a
  jet-A-burning airplane. Also, because they lack an ignition source to
  keep their fires lit, diesels are restricted in how high they can fly,
  even with twin turbochargers and hot glow plugs — although this too
  could be a temporary issue that goes away as diesel experience is
  gained.

An article from AOPA in 2014 indicated some of the prices to replace the AvGas burning engine in an airplane:

A CD-135 costs \$55,000 to \$60,000 in a gasoline engine replacement
  scenario (a Cessna 172 replacement engine), including all necessary parts (such as a new propeller,
  engine instruments, engine mounts, and other parts) depending on the
  aircraft, while the CD-155 costs \$63,000 to \$70,800 for the same
  initial installation kit (dollar amounts converted from Euros). A
  replacement CD-135 costs a little over \$40,000 (excluding taxes,
  shipping, and labor), while the replacement CD-155 would cost just
  under \$46,000 (with the same exclusions).

A (dated) analysis (from 2008) indicates this kind of math (when the TBO was 1200 hours, they now have a time between replacement (TBR) of 2,100 hr):
Cost of replacement engine (Diesel):    $51,150

Inspected gearboxes (3):    $23,500 ($47,118 new)
Shipping: $1800
High pressure pump: $1412 ($5550 new)
Rail valve: $651
Feed pumps (3)  $1255
Clutch (3) $1443
Clutch shaft (3)    $1200
Alternator: $1426 ($2985 new)
Scheduled labor $1800
Unscheduled labor   $5000
Total: $90,637
Hourly engine (1200 basis): $75.53
Total hourly with fuel: $101.03

Lycoming IO-360 REM

Cost of replacement engine: $25,160
Top overhaul at mid-time: $8000
Unscheduled maintenance: $5000
Total: $38,160
Hourly engine (2000 hours basis)    $19.08
Total hourly with fuel: $59.58

One could compare this to a similar analysis that you might do when considering a hybrid car vs. regular gas-only engine. When is the pay-off for using less gasoline compared to the additional base price of the car?

If fuel cost or availability of 100LL is a major concern, consider that a good many existing planes can easily be converted to run on auto gas.

As an additional point, I was at the airport today (June 2017) and there was only a 20 cent difference between Jet-A and 100LL. The price difference in the US isn't painful enough to really make this an urgent thing to change. I know in other parts of the world it is not the case, and that seems to be where the market is right now for Diesel-powered pistons.

Also prices seem to depend on a lot more than the basic cost of fuel.  For instance, buy your Jet-A at RNO and you'll pay 5.19/gal.  Go 20 miles south to Carson City, and it's 2.99/gal for self serve.  100LL is 5.74 at RNO, 4.45 at CC: http://www.airnav.com/fuel/local.html

Because nobody wants to buy expensive new engines for their 40+ year old planes?  Because there's a significant cost to developing & certifiying diesel engines for light planes, but only a limited market?  Because the cost of fuel is only a small part of the cost of buying and operating a light plane?
OK, since you want some numbers, Google gives the cost of a new Lycoming O-360 as around $80K, e.g., this one from Air Power Inc. I haven't found prices for a diesel equivalent, but
one might reasonably expect the cost of an equivalent certificated aircraft diesel to be at least similar.  Indeed,
an article from AVweb says "...a certified civil diesel engine would cost more than twice as much as an equivalent gasoline engine...".
Now if you check Trade-a-Plane for Cherokee 180s (I use this as an example because it's my plane), you find them going for $30-55K.
Now why would anyone spend the (Dollar sign)80K it would cost to put a new  diesel engine in a (Dollar sign)40K plane, in order to save a few bucks an hour on fuel?  Or if we're talking about new production, why would manufacturers increase their manufacturing cost by maybe the same $80K?
PPS: If it's the cost of 100LL that's a concern, many light aircraft can run on mogas.  There's an STC for the Cherokee 180, which we applied many years ago.

I believe this answer can be improved by expanding it. At its current state, it is half-way between a comment and an answer.

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review

@Simon: How does it not provide an answer?  "Because it would cost a lot of money for small benefit" seems to be a complete answer.

Yep, on reflection you're right.  Vote withdrawn.


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Can one country really ban another from using its airspace?
Consider the recent restriction by Saudi Arabia on Qatar Airways flights, which prevents Qatar flights from flying over Saudi airspace. Qatar now has to use longer routes and go fly around the land mass. Does the ICAO not prevent Saudi Arabia from this kind of behavior?

Yes they can.
There was an attempt to allow one to pass over a country freely with the Freedoms of the Air however this is not a blanket thing and not everyone partakes.

....As of the summer of 2007, 129 countries were parties to this
  treaty, including such large ones as the United States of America,
  India, and Australia. However, Brazil, Russia, Indonesia, and China
  never joined, and Canada left the treaty in 1988. These large and
  strategically located non-IASTA-member states prefer to maintain
  tighter control over foreign airlines' overflight of their airspace,
  and negotiate transit agreements with other countries on a
  case-by-case basis.:23 Since the end of the Cold War, first freedom
  rights are almost completely universal.:151 Most countries require
  prior notification before an overflight, and may charge substantial
  fees for the privilege (see the wiki article for references)

But what about Bahrain, UAE, and Egypt, which are parties to the IASTA along with Qatar? Aren't they required to allow Qatari planes to transit their airspace?

It seems the legislation is very much op-in and it is not in way binding thus a country can theoretically back out or not abide as it sees fit since it seems there are not a ton of enforcement mechanisms.

And even when a country is a signatory, that doesn't mean they can't have legitimate reasons to deny access to specific flights or groups of flights based on risks to national security.

@jwenting Very good point, acually, IIRC, if one EU country bans certain airliner or country from operating flights in the country, they are banned from the whole EU. Of course, based on safety doubts.

Qatar Airways CEO seems to disagree: https://youtu.be/qRVjBfk848Y

He can disagree but in the end of the day its up to the nations not the CEO of an airline.

Does the ICAO not prevent Saudi Arabia from this kind of behavior?

In principle yes, by article 9 of ICAO Chicago Convention on International Civil Aviation.

Each contracting State reserves also the right, in exceptional
  circumstances or during a period of emergency, or in the interest of
  public safety, and with immediate effect, temporarily to restrict or
  prohibit flying over the whole or any part of its territory, on
  condition that such restriction or prohibition shall be applicable
  without distinction of nationality to aircraft of all other States.

This would apply to any ICAO member State, which includes Saudi Arabia.

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sort: votes


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Can you safely operate a 777 with diesel?
Is it possible to safely operate a Boeing 777 on diesel instead of Jet-A? Are there any regulations that prevent this? Would it cause any damage?

The other question (https://aviation.stackexchange.com/questions/12184/what-are-the-differences-between-fuel-types-comparing-with-vehicles) is not a duplicate of this question because the answers there do not answer the question here. There is no answer there which states whether or not it would be safe to operate a 777 on diesel fuel, or whether or not that would cause any damage.

JetA, diesel, kerosene, fuel oil are all 98% the same.  Shouldn't be a problem at all.

Unfortunately your question is overzealously marked as a duplicate.  Please find the approved fuels for any specific model aircraft on the Type Certificate Data Sheet (TCDS).  Here is a link:  http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8bff0e63469dd8eb862580190055ffa6/$FILE/T00001SE_Rev40.pdf

@STWilson thanks for the link, unfortunately cannot find any mention of diesel. So, I'm assuming it's not safe. Hopefully, unmarking the duplicate would result in someone being able to answer the question.

Not being certified does not necessarily make it unsafe, although it would be illegal, and one can make an assumption that it wasn't certified because it isn't safe, however it could also just be because there isn't enough demand for it...

No. The fuel system would risk to clog up with gelled diesel fuel in the low temperatures at cruise altitude. If you had omitted "safely" in your question, the answer might be different.
Before I repeat what others have written before, I refer you to this excellent answer by @voretaq7. The essential part is:

Why don't we burn highway diesel or heating kerosene in a 747? In a
  word, purity. The additional controls imposed on Jet-A fuel by the
  associated standard produce a product with well-known properties. When
  you fuel a plane with Jet-A you can be confident that fuel won't
  freeze in the tanks at altitude (at least not unless you cold-soak it
  below -40 degrees). You also know the fuel will be "clean" and won't
  gunk up fuel filters or leave deposits inside the combustion core of
  the engine that can cause problems later.

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Why isn't the APU a standard diesel generator?
Why isn't the APU a standard diesel generator? Jet-A and diesel are interchangeable (with the addition of a lubricant). So why not use a cheaper piston engine as opposed to a jet turbine?

V.S.

The APU also provides bleed air and/or hydraulic pressure.

And why the main engines are turbines instead of piston engines? The answer is same.

the title says "Why isn't the APU a standard diesel generator?" but the text says "So why not use a cheaper piston engine as opposed to a jet turbine?". which one is it? as there is a big difference between these two questions.

@JOW: The question is perfectly understandable to me, and has been answered.

@JOW Because "piston engine" includes diesels, while "jet" or "turbine" excludes both.

Try to restart a diesel generator at 30,000ft.   There isn't enough oxygen there.

@Agent_L: In fairness, one could build a turbine engine that ran on diesel, which would then be a turbine diesel engine.  Not a turbine Diesel engine (as it wouldn't be using the Diesel cycle), but a turbine diesel engine (as it would be burning diesel).

Weight.
Piston APUs for trucks are designed for frugal and quiet operation. This one produces 5.2 kW electrical power and weighs 375 lbs.
The APU for the A320 and B737 is a noisy screaming unit that produces 90 kW electrical power, 445 shaft kW. It weighs 375 lbs as well.

The main difference is in the weight of the engine itself. The turbine engine of the A320/B737 APU produces 445 shaft kW and weighs 145 kg. This diesel engine also produces 450 shaft kW and weighs 1542 kg.
Power-to-weight ratios:

The turbine produces 3.1 kW/kg engine weight.
The diesel engine produces 0.3 kW/kg engine weight, it is a standard industrial machine and not optimised for weight.
The Rolls Royce Merlin was very much optimised for weight, it used aviation fuel (gasoline) and produced 1.58 kW/kg

The APU is also a pneumatic source for running the packs and starting the engines, which favors the turbine as well.

..and, if an off-the-shelf diesel engine was used, it would require diesel fuel, rather than aviation kerosene.  Then you have an exra fuel tank and an extra refuelling operation.  I'm sure that a diesel could be designed to run on the jet fuel, (after all, both diesels and gas turbines are compression-ignition), but off-the-shelf mass-production engines are cheap, a special 'APU diesel' would not be:(  'Jet-A and diesel are interchangeable' - not according to my source;)

@MartinJames There was a bloke in Germany who drove his diesel car on  cooking oil he collected from snack bars. The car wafted smells of fried chips when he drove, he just needed to filter out some of the crusty bits. And anecdotal evidence exists of airport employees who drive their diesel cars on jet A1 no problem. The old diesel engines were not very particular it seems, don't know about the high performance modern ones though.

Would freezing temperature be another reason to avoid diesel?

@Koyovis: not just one guy. For example, in EMEA, a rapeseed oil is very popular in gastronomy and double-use it (and similar) as a fuel is really seriously researched - http://papers.sae.org/2004-01-1858/ etc

@Hugh Diesel gels at about -10°C, Jet A freezes at around -40°C, Jet B around -60°C. Feed jet fuel to a diesel engine and there shall be no gelling...

Even if you compare a diesel generator with no enclosure, you get 0.05 kW/lb, compared to 0.25 kW/lb for the turbine.

Jet-A will blow a diesel engine if it cannot tolerate the additional stress of higher octane combustion. This can be fixed with bulking additives mixed into the fuel line.
You have several thousand pound foot of forced induction already from flight itself, so you can design a system that will intake far more air and output far more power in-flight, but any system not built for it will go bang pretty fast. Off the shelf APU's are designed for use at rest, and pointing their intake out of a plane window is probably none-too clever.

@user1901982 simple, low cost modifications to a diesel engine would make it perfectly capable of running on jet-A.  It still wouldn;t be a good APU.

Late comment: All modern military tank and most other AFV diesels are designed to run smoothly on Jet-A, specifically for fuel commonality reasons. Some military diesels can even run on gasoline. Fuel is not a problem at all for diesels. But they're still heavier than turbines.

@Therac not for turbines either.

Three words:  They’re much heavier.   Gas turbines have a very high power to weight ratio As opposed to reciprocating diesel engines. So for the needs of an airplane which requires large amounts of electrical and hydraulic power in order to operate, a gas turbine makes a lot of sense for use as an APU.

That's four words.

A primary reason, aside from weight considerations, is that a gas turbine APU has a built in air compressor - the compressor stage of the turbine. As such, it can supply air under pressure, or bleed air, just as the main engines can.
Bleed air is used for several purposes on an airliner. It is used not only to pressurize the cabin while in flight, but also serves as an air conditioner or heater, as the climate dictates. The APU can operate the climate control system on the airliner when the main engines aren't running.
Bleed air is also used to start the main engines. One running engine can start all of the others - the main engines have a small turbine that uses the pressurized bleed air to spin the main turbine up to starting speed. Or... the APU can also supply that bleed air. It is not uncommon to use bleed air from the APU to start the main engines, such as when an airliner has shut down its engines while waiting on the taxiway due to extended delays.
In some cases, APU bleed air may be the only option: BA flight 9 used APU bleed air to restart its engines, when all four had been disabled by volcanic ash.
So one reason gas turbine APUs are used on airliners is that they can supply the bleed air that is used for several purposes on the airliner, when the main engines are not running.
A diesel generator would have to power a separate air compressor to do the same, and that's more weight, and another thing to break or need service.

You need to look at the overall picture. Yes, a diesel is cheaper, but it will weigh more and be less reliable. Also, the operating time of an APU is rather a small fraction of total airframe operating time, so it will mostly be a dead weight.
To arrive at a number representative of overall cost, add to the acquisition cost all the maintenance and all the fuel needed, not only for operation, but also for lugging the APU around. If you need a handle on the weight-induced amount of fuel, use the Breguet equation. Here is an answer where it is used to calculate the extra fuel needed to have windows in the fuselage, and here it is used for a partially loaded A320.

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Do airline transport pilot trainees ever fly a passenger-less aircraft?
Do airline transport pilot (ATP) trainees ever fly an empty aircraft? Consider the example where a pilot is under training to operate a 777. Would the pilot ever fly the real aircraft without any passengers? Or is training only limited to simulation?

Both answers concetrate on type rating for existing pilots. Do you ask for existing pilots or people who want to get the air transportation pilot license? Do you ask about smaller aircraft during the basic licenses or do you assume that is finished already?

AS operates cargo-only aircraft, of the same type as their passenger aircraft (737).  I have no idea if cargo flights are used for training in particular, or if they are just bid as regular routes.

When pilots are trained for flying in an aircraft type they have not flown in before, they go through type rating, then line training. During the type rating, they learn where all the instruments and buttons are, what starts which system, how the plane behaves, how to land and auto-land etc.
During line training, they spend time in the cockpit together with an instructor pilot, usually a senior captain. Most airlines have a 3-person crew in the cockpit when a new F/O is receiving line training. This training is about the airline specific bit of flying, company procedures etc.
Note that before going to type rating, the pilot already has at least a commercial flying license: they can fly already. Depending on the country, the type rating can take place in a Level D simulator for 100%. Some countries still require a couple of actual flights in an aircraft, but there is an increasing trend to use Level D simulators only, for two reasons:

Back when the airlines paid and arranged for type ratings, it was relatively simple for them to arrange for an aircraft for a training flight, empty or not. But now a majority of type ratings is self funded, how does a student find the finance to charter an empty aircraft?
The realism of Level D simulators is incredible. My office used to be not far from the simulators - every once in a while I would hear the siren for the sim coming down at an unscheduled time, for an unscheduled break: the stress level inside is real, you reckon that you are really 30,000 feet up with an engine on fire, alarms sounding, actual (non-toxic) smoke entering the cockpit, etc. After clearing the emergency, some students needed time to reflect.

Boeing predicts that we need 30,000 new pilots every year for the next 20 years. How do we streamline it such that all competent persons can become pilots, not only people with enough money to charter a plane?
As @user71659 points out, at airlines that only fly widebodies, standard entry position is a second officer/relief first officer/cruise pilot on a long haul plane like the 777. (Cathay Pacific, Singapore Airlines, Emirates, for example).

So nowadays one can start from ground zero and end up flying Boeing 777 without stepping into the actual airplane at all?

@GeorgeY. No, they can go from 'Can fly a 737, CRJ, or other smaller jet' to 'flying a 777 with passengers but supervised' without stepping in a 777. I'm not sure if you'd need a jet rating, or if you could technically come from something like a Q400.

@GeorgeY. Usually a B737 or A320 first.

@GeorgeY. Yes. Standard entry position is a second officer/relief first officer/cruise pilot on a long haul plane like the 777 at airlines which only fly widebodies (Cathay Pacific, Singapore Airlines, Emirates, for example).

@user71659 But those airlines still send you through primary flight training somewhere where you're flying a real airplane first, right? At least I would certainly hope so.

@reirab Yes, but usually nothing bigger than a twin engine piston plane.

The answer depends on which country you are in. Under FAA regulations (and those countries that generally follow FAA rules), there is no requirement for you to actually fly the actual aircraft before taking passengers on a trip.
Under EU/EASA regulations, there is a default requirement, which is flown on a aircraft with instructors and fellow student pilots. This is called "base training".
AMC2 ORA.ATO.125(k)(1) states

With the exception of courses approved for ZFTT, certain training exercises normally involving take-off and landing in various configurations should be completed in the aeroplane rather than an FFS. For MPAs where the student pilot has more than 500 hours of MPA experience in aeroplanes of similar size and performance, these should include at least four landings of which at least one should be a full-stop landing, unless otherwise specified in the OSD established in accordance with Regulation (EC) 1702/2003, when available. In all other cases the student should complete at least six landings.

European airlines want to follow the US model since the actual flight time is expensive, hence the Zero Flight Time Training. If the specific airline has a ZFTT approved course with a Level D full flight simulator, a pilot with at least 500 hours of multi-pilot aeroplane experience can skip the actual flight if their first four flights are also done under a specially approved program.

"there is no requirement for you to actually fly the actual aircraft before taking passengers on a trip." This is just for a type rating in a new airplane, right? I'm pretty sure you can't get an ATP certificate in the U.S. without (a lot of) actual flying in a real airplane.

I read it first as at least four successful landings and giggled more than I should have.

The other answers describe the use of simulators, and I don't dispute that.
But, earlier this year, there was a documentary by EasyJet, where they showed how their new pilots trained, and they had to go through a couple of touch and go in an empty aircraft before they started flying with passengers. So it likely depends on each airline's policies.
For a slightly less clear example, this post by Air Canada implies that the new B737MAX is being used for training this weekend.

They were likely becoming pilots. Other answers are about existing pilots learning new aircraft.

@VladimirF: you don't "become a pilot" in an A320.

Technically not. But it is a one long integrated programme from zero to the cockpit of A320. But you are right, it is the type-rating phase of that programme, although it is the first rated airliner type for those pilots https://careers.easyjet.com/generation-easyjet-pilot-training-programme-open-for-applications/ This is what I meant. They are new pilots, not just learning a new aircraft.

I agree. Although if you see the Air Canada example, it seems to imply that they are learning the new aircraft without passengers.

@MartinArgerami In the case of a new type to airline, as in Air Canada, they are training more than pilots. Regulators require for a new type to be introduced to a fleet that everybody involved be trained, including mechanics, dispatchers,  emergency services. There are commercial reasons too, the airline wants to test their computer systems, make sure they have the proper ground handling equipment and catering setups. Something as simple as an airport didn't get spare safety cards can cause headaches once in service.

All type rating training would be done in full motion simulators.  The problem with doing it in the real thing is that it is prohibitively expensive.  Also sims allow pilots to run through emergency scenarios - and sometimes allow them to fail and crash - in order to teach key points and reinforce training.  Large commercial airplanes are rarely flown empty; the only examples I can think of are test flights after maintenance has been performed or on ferry flights to a departure city.  When I interned at Boeing as an engineer in 2000, the only empty flights once the airplane was purchased were short ferry hops.  One airline bought a 777-200, thence flew it form KPAE 50 nm south to KSEA, where, within an hour, it was fully fueled, catered, loaded with passengers and flight crew and departed on a polar flight to Moscow, Russia.

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text:
What is this black symbol on a VFR chart?
What is this black symbol near KLBE VFR chart?

It, along with other symbology, is listed in the chart's legend

It appears to be the old Hi-Way drive in theater, given its placement near the highway and direction. It may no longer be such a good landmark as it closed in 2011, though the distinctive clearing is still visible.

An obstacle, an "Outdoor theater".https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/aero_guide/#sectional_radioaids

An outdoor theater.  Used as a VFR waypoint.


text:
Is the increased humidity on modern jets artificial?
Aircraft manufacturer’s including Boeing and Airbus have emphasised on greater passenger comfort owing to an increase in humidity on newer jets such as the 787 and A350 artificial? Or is it a direct result of a greater cabin pressure?

A Reuters article confirms the humidity just comes from the passengers, on the 787 at anyway:

(...) the air is dry and moisture comes mostly from passengers.

And this Flight Global article:

(...) the system does not add moisture through active humidifiers.

This APEX article has no discussion of higher cabin pressure being an influence on humidity.
Lastly, this Business Insider article says Boeing indicates the higher pressure alleviates the feeling of mountain sickness that can come from being at 8,000 ft vs 6,000 ft.

[S]ince there isn't a perfect one-to-one correlation between altitude and jet lag, Boeing has taken additional measures to mitigate the symptoms. These measures include an increase in cabin humidity as well as a new air-filtration system.

So, it's real humidity, and not really an effect of cabin pressure.

How's that last change? It was easier to see what y'all had been doing with the last set of markup changes made.

Note your linked Flight Global article says "Airbus offers such [active humidifier] equipment as an option for first and business class on the A350.", which is relevant for the question.

There may be two factors at work.  First, there may be less air exchange, which would leave more moisture in the aircraft from people.  Reducing air exchange reduces the power required to pressurize the aircraft.  As I recall the 787 is a no-bleed system, with electrical compressors utilized, resulting in a claimed 3% fuel efficiency.  Accordingly, I would expect that a system goal would be to minimize air exchange, which would in turn minimize power consumption. This would result in more retained water vapor.
Secondly, atmospheric pressure impacts dew point, which relates to our sensation of humidity.  A psychometer reading is dependent upon atmospheric air pressure, and is often adjusted for ambient pressure at altitude (for example in cities at higher elevations).
I haven't worked out the numbers, so this is a matter of unsubstantiated but dangerously informed opinion.

Coming with some ECS/Pressurization background in engineering tech support, the only factor I can think of where higher pressure differential would influence humidity, which is all coming from passengers, would be related to leak rate of the pressure hull (they all leak, mostly through door seals etc).  I might expect higher differential to result in a higher leak rate, which would result in more inflow to compensate, which could reduce the humidity level some amount.   However, I suspect that this effect, from say going from 8 to 10 psi (or whatever the 787 uses), is pretty small and if the 787 is using a sophisticated control system that manages inflow/outflow to control humidity as well as pressure, the point is probably irrelevant.

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text:
Why do propellors have white markings on their tips?
Why do propellors have white markings on their tips?
Here are a couple of examples:

It is so you will see a circle when they are turning.  Without contrasting bright tips turning propellers are invisible, and pose a grave risk for someone who is deaf, wearing heavy hearing protection, or distracted by other noises.

ie: in moving pictures

@J..., excellent video!  Do you mind if I add that to my answer for completeness?  (It was late last night when I answered...)

Sure.  It's not mine - I just grabbed a link from shutterstock.

On second thought, I think links are discouraged in answers because they can expire and break.

Yes, but that's largely if the substance of the answer is contained in the link.  In this case it's just supporting material - the answer stands alone without it.  That said, there are also some nice stills in the dupe so...


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How do airplanes measure cross-wind?
Are aircraft equipped with any instruments that measure actual crosswind velocity during a flight? What is that instrument called and is it used by autopilots to apply wind correction?

Worth noting that when aircraft are vectored by ATC they're given a heading which includes any required corrections. If ATC says Heading 220 they mean your nose should be pointed at 220 - you aren't meant to second guess and add any corrections. I'd wager most use of autopilot is by aircraft operating under such conditions so I doubt any apply any crosswind corrections

@Dan If you tell the autopilot to fly a given heading, then it flies the given heading (of course without any correction applied). But some autopilots also allow flying a given track instead of a heading (e.g. on an Airbus FCU you get that by pressing the HDG-TRK V/S-FPA button), which then has the correction applied.

What sort of aircraft, and under what conditions?  For most GA planes flying VFR, it's called "looking out the window".  (Especially when landing.)

There is not a specific instrument for this, because it is not directly measurable.
Most modern aircraft have digital sensors for heading and airspeed, and their GPS/IRS will know ground track and ground speed. Any difference between those two vectors will be due to wind, and it’s a simple calculation to determine the wind vector’s direction and magnitude.
In practice, pilots (or autopilots) know the desired track, so we simply adjust where the nose is pointed until the actual track matches the desired one. There’s no need to know the exact winds.
I’ve flown planes with a wind display, and the only thing I really used it for was when practicing engine failures, to maximize glide distance with a tailwind and then minimize landing distance with a headwind. Otherwise, it was for entertainment value only.

Yes, it is called a driftmeter and consists of a telescope aimed straight down at the ground. It has a set of scribed lines projected  onto its field of view which the navigator can rotate so the scribes exactly follow the paths of objects on the ground. The navigator then reads off the resulting angle between the plane's axis of motion and the scribe lines. Knowing the plane's airspeed, the navigator then solves the resulting wind triangle to obtain the crosswind component.
This is a simplified explanation; in practice the navigator also needs to know whether the plane is in a tailwind or headwind to solve for the exact value of the crosswind.
Today, radionavigation systems have eliminated the driftmeter from common use.

Your last sentence is weird. Driftmeters were used to improve dead reckoning in areas where radio navigation isn't available (e.g. over oceans), so radio navigation hasn't eliminated the driftmeter. I think you mean inertial navigation and GNSS have eliminated it.

Today drift is measured by the ADIRU comparing air probes data and accelerometers data.

Not crosswind per-se but wind in general is calculated on-board by comparing aircraft internal data with GPS data. Your aircraft knows it's current heading and most computers can give you a pretty accurate educated guess on your True Air Speed. If you compare both of those with your Ground Speed and Track (this is, the actual lateral flight path of your aircraft) then you know your Drift and the speed difference.
This is now simple math. "Aircraft" Vector + Wind Vector = Flight Path Vector so Flight Path Vector - Aircraft Vector = Wind Vector.

Modern airliners have Flight Management Computers that automatically calculate the crosswind component and then apply any necessary course corrections in any Lateral Navigation mode.
Many can also display the current crosswind component.
Here is an example of a B777 FMC that shows a right crosswind component of 28 knots in the upper right corner.

Airplanes with FMS systems normally display calculated wind direction and speed on the navigation display.  It's simply based on the differences in heading vs track, and true airspeed vs groundspeed, worked out within the FMS computer.
You can watch it in action in real time if you fly across a jetstream on a perpendicular track. You will see the heading change several degrees upwind but with little change in groundspeed because the wind is at 90 degrees, but the FMS will calculate the velocity of the jet from TAS and the heading vs track change, and you'll see the wind velocity rise from, say 30kt, to 90 kt or more, with the airplane turning into it to maintain track as you enter the core of the jet, then back to what it was originally when you exit the other side.


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Are gate ramps sloped?
If you’ve ever seen an airliner park at its gate, you’ll likely note that sometimes it will move beyond slightly beyond its designated parking line. However, you may see that after the brakes are applied the aircraft moves back in “reverse” onto the correct parking line. It appears to me that this is as a result of gate ramps being at an angle. Is this correct? If not what are other possibilities for this phenomenon?

I've never seen (or felt) an aircraft move in reverse after coming up to the gate (and I fly a lot). I'm assuming that you are asking if the concrete part the aircraft parks on is at an angle? Then no, it is not (typically).

What you may think is missing the "mark" is possibly not for that model aircraft. There are usually 4 or five marks - but not for all aircraft. The marks are often annotated with certain aircraft like "737" and when a 757 is parked, the ground crew knows they need the nose 4ft ahead of that mark. A perfectly flat surface is undesirable for moisture, de-icing runoff, and fuel spills.

At most airports, the slope is away from the building for water drainage mostly.
This results in a slight rearwards movement when the pilot releases the park brake and the wheels roll back and compress slightly when they rest against the chocks.
This is a pain when it comes time to pushback as the airplane needs to be towed forwards a bit to enable the rear chocks to be removed.


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How do fighter jets pre-flight so quickly?
Military fighter jets can get in the air and to their target in minutes and faster than almost all other aircraft. How do they achieve this considering that a normal pre-flight alone takes ~10-15 minutes?

(Source - My many years on fighter jet flightlines. F-111E, F-106, F-15, F-16)
Peacetime alert
The designated jets are fully preflighted. Munitions fully loaded. INS aligned, IFF code laid in, most but not all of the safety devices removed. The jet is ready to go except for the pilot and engine start.
Assigned alert pilots and ground crew are hanging around. Alert hangar right next to the runway.
Can get in the air in under 5 minutes.
We had to scramble F-106 from Griffiss AFB more than once, to escort Russian Bears down the East coast.
Elevated threat
All of the above, except the aircrew may be sitting in the seat. Rotate pilots every X hours.
Wartime or imminent threat
All of the above, but engines may be idling. All safety pins pulled.

Typically you would do a preflight like this, but it's obviously different from place to place, depending on local requirements.
Before placing the aircraft on quick response status, you would do the normal preflight procedures like inspecting the aircraft exterior, checking cockpit, following your pre-engine start check, and starting the engine.
After this, during the post engine start check, you don't remove the ground safety pins.
The aircraft is now ready for scramble, per local policies and directives - and the only thing the pilot needs is for the flight engineer to remove the safety pins.
So TLDR: They do the preflight before placing the planes on the quick response status.

@ymb1 Pre-started without the pilot in the cockpit. But it's very different from place to place depending on local requirements. You can definitely find places where the engine is not started, but just prepared for start. This of course adds time before takeoff, due to the post engine startup check :) Hope this helps!

The concept of keeping engines running on idle sounds insane and inefficient considering the fuel burnt, lifespan of engine and overall operational costs!

@TayE The entire point of “quick response” aircraft is to be ready to intercept inbound hostiles likely moving at supersonic speed. Waiting to start your engines until after detection means the hostiles get inside your security perimeter before you can engage and maybe even destroy you while you’re still on the ground. That’s much worse than wasting a little fuel idling the engines.

Presumably there is another level of readiness in which the engine is not started, and which takes slightly longer to get into the air, but which can be maintained for hours.

@DJClayworth, yes, the alert posture is highly dependent on the threat level.  Sitting on the ground with turning would be extremely rare, and would mean a strike is imminent, or you are spare for an airplane already launched or planning to launch.

@Noddle, is there any post-start checklist to speak of? My understanding is that with turbine if it is stable in idle with normal temperature and oil pressure, it is good to go. Even airliners start engines and basically immediately commence taxiing. So it should be just the half minute to minute start cycle.

@JanHudec Well, according to the F-16 flight manual, it's ready to go as soon as the pilot is in and ready!


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What is the technical name of the electric window dimming system?
I have recently flown from Mexico City (MMMX) to Tokyo, Japan (RJAA) in a Boeing 787 of All Nipon Airways (ANA).
The plane had an electric system for dimming the windows.
Does the window-dimming system have a technical name?

Related: Electrochromic interactive panel, probably liquid-crystal gel.

From a Boeing article:

Electro-chromatic dimmable windows

It's generically described in the article as being an electronically controlled and can dim or lighten the cabin at the push of a button. They claim 70k cycles or 20 years of service
Gizmodo provides a succinct description of it's operation

The dimming effect is the result of an electrified gel sandwiched between two thin pieces of glass. As the electric current increases, the gel darkens and as it drops, the gel lightens.

The maker appears to be Gentex and they have a variety of electric dimming window patents but it's not clear which one is used in the 787

Boeing's patent US20050200934 A1 calls such a system 'Electrochromic device control system'. From the patent:

Electrochromic device control systems and methods are disclosed. ... Each transparent window has an electrochromic device operatively associated therewith. ... In one particular embodiment, a window dimming control system in accordance with the present invention may advantageously be incorporated into an existing cabin services system of a passenger aircraft.

oooo! thanks :D


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What surface materials do airplanes use to reduce friction?
Full swimming body suits were banned from Olympic Games a few years ago because some materials have less friction than skin and contestants that could not afford gear to increase their performance were disadvantaged.
However, low friction materials could benefit many industries including aviation. Are there any special surface coatings either experimental or used by manufacturers to improve the aircraft performance and decrease drag?

In a way, yes. By using smooth metal surfaces with countersunk rivets, modern aircraft use a surface with low friction already. In the past, wooden structures were varnished to give them a smoother surface. In the second World War, German crews would polish the normally matte paint of some of their airplanes to eke out the maximum in top speed.
There have been several attempts in the past to improve the smooth metal surface. The most attention was heaped on riblet surfaces, a grooved plastic foil the surface of which was inspired by shark skin. Since the 1980s several experiments were made with partially riblet-covered airplanes, boats or wind turbine blades. The gains of up to 8% in drag reduction are real, but the application and maintenance of riblet-foil covered surfaces made the technique impractical.

Shark skin surfaces (picture source). The common understanding is that the streamwise grooves will suppress oscillations in the flow and reduce friction drag. The overall effort to maintain this surface has so far been considered too high in order to achieve the small reduction in drag that is possible with a grooved surface.
And now for something completely different …
Monocrystalline solar panels would result in a polygonic surface and need to be embedded in clear resin to produce the desired curved outer surface. Solar foils are much easier to apply and weigh much less, but also have a lower efficiency. So far, only experimental airplanes have used solar panels on their skin and the integration of those panels was a major part in the overall cost of those airplanes.

The Gossamer Penguin used a rather clumsy way to add solar panels in order to avoid the major work of integrating them into the surface (picture source). It should be obvious that this way of integration adds both drag and weight.

Solar panels of the Solar Impulse II (picture source). It used a rectangular wing planform to make the integration of the solar panels easier since the same mold could be used for all wing panels. Now the solar panels do not add viscous drag, but the weight of the panels, their wiring and the clear resin needed for the smooth, curved surface adds weight which causes an increase in induced drag.


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Why use different data bus for civil and military avionics?
There are various type of data bus in aviation, the two most common in the '90 were ARINC 429 for civil aviation and Mil 1553 for military applications. They are not very different one for the other, the Mil is a little more complex.
My question is: why use two different data bus? The physical cable is the same (as far as I know, you can correct me if I am wrong) but the protocol is different. I think that what a data bus must do is the same in civil and military avionics, am I wrong?

My understanding (from integrating electronics into aircraft platforms) is that 1553 is used in civilian avionics devices.

The avionics I have worked (all civilian) with use ARINC 429 because that is what is predominately used on the aircraft. Hopefully someone might have some historical insight into the original aircraft that used Mil 1553 vs ARINC 429. I've also seen RS-232/422/485 used as the electrical standard

@mongo I concur, ARINC-429 is for civilian use having worked with all major air-framers and major airlines around the world.

The two are actually quite different. ARINC429 is 32 bit standard while 1553 is 20 bit, encoding the 1 or 0 is bipolar return to zero vs Manchester II bi-phase, simplex vs time division multiplexing, 1553 needs a bus controller, bit rates are wildly different... could go on...

There is actually quite a lot of difference between ARINC-429 and MIL-STD-1553.  They are different because they were developed by two different groups with different needs.
Both started in the 1970's. Before then there was almost no digital data of any kind on a an aircraft.  It was almost all analog or discrete. The biggest issue was noise and interference of the signals. The introduction of microprocessors in the early 70's opened up the option for reasonably priced digital bus technology.
The MIL-STD-1553 bus was a major component of the F-16. Like most military programs, this was a push for maximum performance. ARINC-429 came out of the Boeing 757/767 development effort. Civilian aircraft certification doesn't like a lot of risk and the simpler bus architecture made it easier to design, analyze, and certify.
Since then there have been a number of new buses introduced into aviation. Some have lasted longer than others. B777 introduced ARINC-629 and Fibrechannel. B787 uses ARINC 664 for the main buses with a large mix of ARINC-429 and ARINC-825 (CAN bus) as well.  There are a number of data concentrators/converters on the aircraft to get data where it needs to go.
The primary reason for moving away from ARINC-429 is that it is a single transmitter/multiple receiver architecture. This results in a large amount of physical wire. That adds weight and requires maintenance. A bus such as ARINC-664, which is based on Ethernet, can significantly reduce wire. The down side is that it costs a lot more and isn't very efficient when all you need is a small, low rate connection to an odd corner of the aircraft.  So you end up with a mix of buses.
And B787 opted for fiber optic cable for the ARINC-664 network to reduce interference from high-intensity radio frequency (HIRF) and lightning.
MIL-STD-1553 is a powerful bus, but it's not as good a fit as many of the newer buses available in the commercial market. The military keeps using it because they have a huge installed base of equipment, it's flexible enough to support their newer functional needs, and commonality reduces their logistics costs.
ARINC-429 sticks around because it's cheap and it has its own large installed base as well.


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Why does a plane shake while passing through clouds?
Why does a plane shake while passing through the clouds?
During my last journey all the other passengers started shouting when the plane was passing through clouds. It was the third time I was travelling by plane and was a fearful experience. Can someone explain what the reason is for the shaking? So the next time I can travel free of fear.

I disagree that this is a duplicate. The answer is not just turbulence, but how clouds are related to turbulence. Clouds are not mentioned in either of the answers to the other question.

The other question is clearly not a duplicate of this one...

In a word, it's called "Turbulence" and in cloud, it is caused by differing air density.
Sciencey bit: The sun warms the earth and causes the air to rise. As warm air rises, it cools at the wet adiabatic lapse rate. Inside of a cloud, this rate is much slower than outside of it. Clouds are more dense than dry air, and the water vapour inside a cloud is not spread out evenly. Combined with the thermal turbulence (the movement of warm air) and the lower wet adiabatic lapse rate (rate of cooling) results in drafts of air through the cloud.
The result to the aircraft is pockets of more and less lift on the wings in somewhat unpredictable patterns. You feel this inside the aircraft as bumpiness and occasional feelings of rising or dropping. Sometimes this can be quite pronounced - this is why you will almost certainly be asked to remain seated with seatbelts fastened.
Very occasionally, outside of clouds, there can be more unpredicatable turbulence which may come as a surprise to the Pilot. This type of turbulence can cause injuries - usually from falling luggage or persons. This is why, even during cruise, the cabin crew and pilot usually suggest you keep your belt on while seated.
In almost no case does any kind of turbulence cause any damage to the aircraft or significantly affect its airworthiness.
Another answer here might be interesting reading for you How dangerous was the turbulence on this commercial flight?
as might What is turbulence, and how does it happen?

Not all clouds cause turbulence. Flying through stratus clouds is generally very smooth.

@MikeSowsun yes, of course you're right. But you could end up caveating every sentence with "except in this case". I was going for the simple explanation. The linked answers are much more detailed.

This is a good answer, but I think @TechMedicNYC is also correct. I've also noticed high frequency vibration of aircraft perfectly correlated with entering and exiting a dense cloud that feels very different from convection turbulence.

@Mike Sowsun: And conversely, you can encounter turbulence when not in clouds - indeed, in a perfectly clear sky.

you should not remark in the answer that the Q should be closed-as-dupe. Just flag it and let the reviewers vote. There is no demerit in asking a duplicate question. We flag them because it is useful to link the questions, makes the knowledge base more searcheable and saves effort on answers because there is already one. I've already cast my vote to close as duplicate.

@Mindwin Had I have found that question before answering, I would have VtC as a dupe. It doesnt make much sense doing that after answering. But you're right, the wording was unecessary - interlinking answers is just as useful (if not moreso) than VtC.

I'm not an expert, but I have a background in mechanical engineering.
I don't believe the turbulence answer is correct for all cases. Yes, turbulence causes shaking and yes, most clouds will contain more turbulence due to thermal effects, updrafts, downdrafts, etc...
However, I'm more inclined to believe the phenomenon the OP is asking about has to do with the density of the medium. The cloud contains cooler air, with suspended liquid droplets. This air should contain more mass per unit volume (that is, higher density fluid). This changes the amount of lift experienced as the plane passes through it. This would produce sudden changes in the amount of lift, causing shaking when entering or exiting the clouds. Furthermore, the clouds are not of uniform density. Pay attention as the plane enters and exits the cloud, you will notice the amount of "cloudiness" varies. This means the plane will be passing through air of varying density while in the cloud, causing the "bumpiness" of the ride.


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How to represent graphically airways and routes?
I need to write a piece of software in order to display on a map flight routes and airways. I would therefore like to know if there is a standard way of displaying this kind of information (in particular the kind of icons used for displaying waypoints, departure and arrival airports and so forth).
For example, by Googling a bit I have the chart shown below:

Could someone point me to any additional sources of information that I could use.
I am particularly interested in the icons/shapes to use as well as the kind of relevant information to show. The idea would be that the map is recognizable at once by a professional pilot and provides him all the relevant information.

Have you looked at the IFR charts and the legends for the symbols used?

I've looked into that before.  Check out the apis on Skyvector, Flightaware, and similar sites.  It's easy to get the URLs from Google F-12 dev tools.  There have a look at the jsons for data structure and source files.

I've got a few .png files of waypoints and such here

ICAO Annex 4 contains guidelines for creating aeronautical charts.
The type of information to be shown and required accuracy of information is defined in the different chapters, depending on the type of chart. You will probably be interested in chapter 2 and chapter 7/8.
Symbology and standard colors are explained in appendix 2 and 3.

I would recommend the FAA Aeronautical Chart User's Guide which is available in both web format and as a downloadable PDF. The descriptions are organized by chart type.
There are several options as airways are depicted differently on different charts. It depends on the primary use of charts.  For VFR charts, the depictions are primarily to show where the airway is (and by implication the expected traffic).  On IFR charts where they airways are normally part of a route, there is significantly more information related to the airway.  Much of that is essential when navigation under IFR.


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Why does an aircraft use less fuel while landing as opposed to takeoff and climb?
I read that the weight ratio of an aircraft after and before landing, was larger than the ratio after and before takeoff. The weight is lost only due to fuel burn, so why does an aircraft appear to consume more fuel during takeoff than during landing? How does the 'ground effect' play a role here?

Ground effect plays very little here.
When taking off and climbing you need to add kinetic energy and potential energy to the plane in terms of speed and height. Getting that energy requires burning fuel.
When landing you want to get rid of that energy. Easiest way is to turn down the engine (or off when something breaks) and let drag slow you down and trade height for speed.
When taking off the plane will also be heavier because it will have more fuel on board. So it takes more energy to speed it up and get it up high.
It's very similar to climbing a hill and descending a hill, going up takes energy and going down means you can coast.


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What are the most common uses of radio communication when flying?
What are the most common uses of radio communication in aviation? I know that many aviators communicate with the people in towers with radio, but what do pilots say to the people in the towers and vice versa? What do pilots and ATCers communicate about.

Related: What ATC entities does a commercial airliner communicate with?

Is it your intent to limit this to spoken communications?

It will be hard to list everything that is said, but I can try to start with some of the basic examples:

Pilot is ready to taxi to the Runway
P: Tower, N12345, has information Tango, at South Parking, ready to taxi.
T: N12345, taxi to runway 13 via Alpha, Delta.

Pilot is ready to take off
P: Tower, N12345, is ready to go at runway 13. Request SouthEast Departure
T: N12345, cleared for takeoff, SouthEast Departure approved.

Pilot wants to cross another airspace
P: Tower, N12345, is 10 miles to the East, 1,500, request transition east-to-west
T: N12345, transition approved as requested.

Pilot wants to approach an airport to land
P: Tower, N12345, is 10 miles to the South, 1,500. To Land
T: N12345, make Left-traffic for runway 17; report a 2 mile final

Radio communication is used to pass information aircraft to ground, ground to aircraft, aircraft to aircraft or whatever other direction you can imagine.  This information could be anything relevant to the flight.  For instance, when flying VFR at an uncontrolled airport it is expected that you announce your intentions while taking off or landing so that other pilots can anticipate what you will do and where you will be.  Crossing areas with no radar coverage you use an HF radio to announce your position periodically because ground controllers cannot see you.  This serves as a method to know you're still alive and allows for at least some level of separation from other aircraft.  Other pilots can also hear these position reports so they know where you are.
When talking to controllers you could be discussing weather, vectors to a destination or geographic point or a number of other things.  Sometimes it may not be relevant to the flight, such as asking the score during the World Series.  Not exactly the purpose of aviation communication, but this sort of thing happens more than you would think.  I've even done late night flights were I would be talking to another pilot heading in the same direction for hours just shooting the breeze.  A couple of times controllers would participate.
These are just examples.  The list could go on and on.

This answer completely neglects to mention the main use of radio: air traffic control.

The most important use of aircraft radio is communication with air traffic control. You already know there is something called tower, but air traffic control is much more than that. With the exception of small private airfields and low level flights in remote areas, pilots are in contact with air traffic control from the moment they leave the gate/parking position, until the moment they park at their destination. Air traffic control decides which way the pilot must fly, how high and how fast. Of course, it is up to the pilot to let ATC know what they want to do, but the pilot is not allowed to simply do it.
Ever been in an airliner approaching an airport? During approach, the aircraft will make a series of turns, eventually ending up on the runway. Every time the aircraft makes a turn, that's ATC telling the pilots to do so. Every little turn, every change in altitude, every speed change - air traffic control instructions, submitted to the pilots by radio.
There are books written on air traffic control, and I think it is beyond the scope of this question to go into detail. I do encourage you to do some research on your own - including on this site. So to summarize the answer to your question: aircraft radios are used by pilots to communicate with air traffic control.

As a General Aviation (GA) practitioner and advocate (AOPA, Hooah!!), I must ensure that Unicom and Multicom communications are thoroughly explained.
Unlike air carrier crew members, GA pilots are required to take sole responsibility for maintaining safe separation distances and attitudes from other aircraft, making dynamic air traffic management command decisions in an array of high paced environments regarding flight procedures and operations, and the utilization of technologically advanced radio communicate  and navigation systems to ensure safe and efficient operations through the air space they are utilizing.
Air carrier crew members are forbidden from engaging in these and many more operational procedures which require decision making capabilities which are independent from the strict, pre-planned, and thoroughly rehearsed guidance provided by air traffic controllers (ATC). These seemingly higher risk operations are only authorized to those pilots who have demonstrated a high level of skill and single pilot crew resource management skills. The vast majority of flights in the US operating in the uncontrolled realm do so under Visual Flight Rules (VFR). Here are the basics of communications in uncontrolled airfields and airspace:
Unicom frequencies are used at airfields or designated volumes of airspace (practice areas, scenic corridors, published transition corridors, etc.) which have no ATC services available. In the absence of a published Unicom frequency, piloted will use what's called the Multicom frequency, which in the US is 122.9 MHz, to make radio calls.
In either case, pilots decide unilaterally how and where they will maneuver their aircraft to accomplish what they are intending to do (practice maneuvers, land, take-off, etc.) In order to ensure all other pilots in the vicinity understand the position and intentions of their aircraft, a pilot will provide "self-announce" radio calls over the designated Unicom frequency (found on charts) when and where appropriate (as determined through training and experience).
When operating in airfield traffic patterns, this is generally done just prior to turning onto the subsequent traffic pattern leg (upwind, crosswind, downwind, base, and final). Pilots however may elect to modify this model based on Unicom frequency congestion and/or local area special procedures.
Pilots structure each individual radio transmission using the following protocol:
Intended Recipients -> Aircraft Type and Registration Number (shortened in most cases) -> Aircraft Position and/or Intent -> Runway (if applicable) -> Location of Intended Recipients
Probably doesn't make much sense, so here are some examples.

In this scenario, we are in a Cirrus SR-20 with registration number N566GL (Totally made up, didn't check the FAA registry, so...yeah might be a 777 for all I know!), and we're parked at an airport in Northampton, MA (7B2). We're going to take one trip around the traffic pattern and land. Let's say we're doing a maintenance test flight, just for funnsies.

I'm not going to spell out what the aircraft is doing with each radio call, just what would be transmitted as some context notes in parentheses if applicable. If the call is answered, I'll put it in there for continuity. Take note of the slight structure variations in the first transmission, when the communication is directed at a specific recipient as opposed to transmissions meant for any aircraft in the vicinity. Also, the phonetic alphabet is used in all radio calls, which I spell out in the initial transmission. I shorten them to single letters for the rest of the transmissions for the sake of brevity. Here we go:

Northampton Unicom, Cirrus 6 GULF LIMA, Radio Check please.
-Cirrus 6GL, Northampton Unicom, radio check loud and clear (or 5 by 5, or something like 'Aircraft calling Northampton Unicom, you're broken and unreadable')
Northampton Unicom, Cirrus 6GL, I have you the same, thank you.
Northampton Traffic, Cirrus 6GL, Currently parked on the west apron, taxiing to Runway 14, Northampton. (Level of detail provided in ground movement Unicom radio calls will depend on local procedures)
Northampton Traffic, Cirrus 6GL, Taxiing onto runway 14 for departure, Northampton.
Northampton Traffic, Cirrus 6GL, Departing 14, Remaining closed traffic (staying in the traffic pattern) Northampton.
Northampton Traffic, Cirrus 6GL, turning cross-wind, 14 Northampton.
Northampton Traffic, Cirrus 6GL, turning downwind, 14 Northampton.
Northampton Traffic, Cirrus 6GL, midfield downwind, 14 Northampton (this is an additional call that may or may not be required based on conditions)
Northampton Traffic, Cirrus 6GL, turning base, 14 Northampton, Full Stop (as opposed to touch and go. Again, not something that is considered a requirement, but is often included by the pilot to assist other aircraft in the vicinity with situational awareness)
Northampton Traffic, Cirrus 6GL, turning final, 14 Northampton. Full Stop.

If needed, pilots can provide estimated distance to runway, especially if that distance would be considered non-standard for that particular airfield or runway. It would sound like this:

Northampton Traffic, Cirrus 6GL, turning half mile short final, 14 Northampton. Full Stop.
Northampton Traffic, Cirrus 6GL, back taxiing 14, Northampton.
Northampton Traffic, Cirrus 6GL, clear of 14, Northampton.
Northampton Traffic, Cirrus 6GL, taxiing from BRAVO taxi-way to west apron for parking, Northampton.

So there it is. Another situation would be announcing to ensure other pilots understand where in a designated practice area you'll be operating and what maneuvers you'll be conducting. These transmissions are often far less structured than traffic pattern radio calls.

BRAVO Practice Area Traffic, Cirrus 6GL will be operating in quadrant 4 between 3,000 and 1,500 feet and will be conducting power on and power off stalls for approximately three zero minutes. Any traffic in the vicinity, please advise. GULF Practice Area.

Generally in these cases, an update call is made every 5-10 minutes while the pilot monitors the frequency for other aircraft position reports that may be a factor.
The last scenario I'll cover is when an aircraft is operating in a designated or published VFR corridor or area. There are a few of these in the US, however the 2 that I have flown in are the Hudson River Corridor in NYC and the "Mini Route" in the Los Angeles, CA area.
The Hudson River Corridor is, in my opinion one of the most unique and spectacular GA treasures found in the US today. I find the fact that it is even still open and used everyday by hundreds of fixed and rotary-wing GA aircraft, none of which are being controlled by ATC, absolutely amazing. Even after the tragic events of 9/11 and then the Cory Lidle accident, the Federal Aviation Administration (FAA), with full support of AOPA and EAA, did not bow to the alarmists who wanted to shut the corridor down to GA aircraft. Before I end my Kool-Aid driven motivational rant, I will say this: If you ever have the opportunity to fly this corridor, don't hesitate to take advantage of it. It is safe, it is structured, it is what GA flying is all about, and the experience is unbelievably surreal. If able, fly it at night as well. It is a completely unique experience in and of itself, and worth every second.
Ok, the other corridor, the LAX Mini Route, is another tool provided specifically for GA aircraft by the FAA. This route, one of a few in that region, allows GA traffic to safely and efficiently cross directly over the top of the Los Angeles International Airport (LAX), essentially bridging two large portions of the LA Basin. At one time, LAX and it's related operations were nothing less than an insurmountable brick wall for GA aircraft trying to get from one side you the other. To do so, GA aircraft were required to conduct an expensive, time consuming, and marginally safe circumnavigation of LAX airspace.
If it sounds like I am influenced by a  favorable bias regarding the FAA, it's because I am. Yes, they can be a tremendous pain sometimes, but by-in-large, the rank and file employees which make up the FAA are dedicated civil servants whose goals are rooted in an effort focused on fostering the most safe, efficient, and advantageous use of the National Airspace System (NAS) by all users. Some are even bigger civil aviation dorks than we are...but I digress.
The radio calls in these VFR corridors are usually depicted on a chart or procedure plate, and often include position reports at certain predesignated positions. The Mini Route is slightly more complex, in that pilots are required to make position reports to various ATC facilities as well as Unicom radio calls as they progress through the route. The Hudson River Corridor is only Unicom calls, and I'm going totally from memory here (check your charts!), but they go something like this:

Hudson River Traffic, Cirrus 6GL is southbound, abeam the Intrepid (aircraft carrier museum) at 900', will report Statue of Liberty next.

So that's my explanation of communications in uncontrolled airspace. Airline pilots, I love you guys, I was just busting your stones way up at the top of this. To be clear, airline pilots are a group of very skilled aviators which represent the true professional segment of the US pilot cadre. I was just being a PIA in the beginning!
Hope this helps!

The first 3-4 paragraphs sound like they came more-or-less straight from a legalese/marketing pamphlet. If so, please quote your source, if not, my apologies - you must speak marketing/legalese for a living...

LOL!! That is hysterical!! No sir, straight from my melon. I'm going to go back and read what I wrote. It was semi-satire, as I was needling any airline pilots who might be reading. Full disclosure, I did write marketing copy and other stuff in the past!

you must have been a very good copy writer! :) /OT


text:
Can we apply landing minimum with ALS when ALS is available with low intensity only?
Can we apply landing minimums with ALS when the ALS is available with "low intensity" only?
For example, the following NOTAM is issued at KABQ:

!ABQ 05/270 ABQ RWY 03 ALS OUT OF SERVICE EXC LOW INTST ON CONS
  1705302145-1706151800EST

In this case, is the applied landing minimum for ILS RWY03 VIS 1/2 or VIS 3/4?
I'm talking about part 121 operator.

Can you link to an actual instrument approach plate? I can't see 1/2 or 3/4 anywhere on the KABQ 03 plates, so it isn't clear what you're looking at and if those plates include any restrictions based on lighting. And are you asking about part 91, 135 or 121? The general rule on approaches is that part 91 has no restrictions beyond what's on the plate, whereas 135 and 121 have some additional rules and also have to follow their OpSpecs (as approved by the FAA).

Thank you for your advice.I'm looking at Jeppsen chart.And I'm talking about a scheduled commercial airliner.I can' t add link because Jeppesen chart isn't free to publish.According to TERPS page 3-16, if HAT is 200ft and non-ALS, applied landing minimum is VIS 3/4.

The TERPS don't deal with LIALS at all -- they punt that to 1.4.2 on nonstandard IFPs, which requires a special study.  Yet, there's no FDC NOTAM out adjusting the SIAPs at the airport. WTFAA?


text:
Can different departure procedures have different transition altitudes at the same aerodrome?
Is it possible for operations and ATC to have different departures procedures with different transition altitudes at a single aerodrome? For example:

SID RWY11 with a transition altitude of 2,000 meter
SID RWY29 with a transition altitude of 2,500 meter

What country/jurisdiction are you referring to?

It is not established in the real world.

I've just never heard of a transition alt being tied to an approach procure

Yea, I have never too. One of the procedure designers has just sent me(cartographer) a draft version of approach procedure. Then logically, I rejected the procedure due to that Transition altitude.

IIRC the transition attitude can never be lower than 3000ft

what do you mean with transition altitude. On an approach you are coming from above, so the transition altitude should not matter to you, transition level is what matters. I suspect you mean something different. Do you mean the altitude at which you fly before you intercept the glideslope?

@DeltaLima In my Country, most of aerodromes do not have SID-ICAO. So Transition altitude is shown IAC-ICAO. That is why i asked that way, i have just edited question into correct way to ask,

So are we talking about when to switch to QFE here or what?

No. The transition attitude in a defined area is fixed. For example, in the USA it is 18.000ft and in many European countries it is 5.000ft. It's impossible to have different transition altitudes at one airport, because that would make it impossible to use vertical separation between aircraft close to the transition layer.

+1 for mentioning it has nothing to do with a single airport. However, I suppose the transition altitude can vary inside one country (in different regions), can't it? In large countries with a variety of terrains like China or India, it would make sense...

@mins Interesting, I've always thought it's primarily defined by area and not by airport.

@mins, “varies from airport to airport” does not necessarily imply that it has anything to do with the airport itself. Every airport is in some sector and if it varies between sectors, it varies between airports too.

ICAO PAN-OPS (v1) 2.1.2.2: "Where two or more closely spaced aerodromes are located so that coordinated procedures are required, a common transition altitude shall be established. This common transition altitude shall be the highest that would be required if the aerodromes were considered separately." – mins 2 days ago
This comment should be the answer for me. Thanks all, Everything wroten here is useful information.


text:
Are there cases of a thrust reverser used on a turbojet engine?
In the case of a turbojet (with no "cold" bypass flow), the airflow being directed forward by an hypothetical thrust reverser can be really hot.
Depending on the location of the engine, this flow may be dangerously redirected towards the empennage and the fuselage.
For instance, for a fighter this would be a hazard for sensors, equipment, payloads including missiles, likely many other elements, and pilots:

General Dynamics F-16C (source: Wikipedia)
Are there turbojet engines fitted with a thrust reverser? Which aircraft are they used for? How is this problem dealt with?

The Panavia Tornado has it: https://aviation.stackexchange.com/q/14705/1467 With a BPR of 1.1:1, does it fit your definition of "turbojet"?

@Federico: It doesn't :-( the idea is anything without handy cold bypass. Interesting case though. Thanks.

oh, then I am not sure there are many being used at all, I think all have some amount of bypass :| (another one is the Viggen: https://en.wikipedia.org/wiki/Saab_37_Viggen#Propulsion )

@Federico: When you say "all have some bypass", do you mean all engines (meaning pure turbojets have all been replaced by low BPR turbofans, presumably for efficiency reasons), or all engines with reverser?

The first: no-bypass engines are no more in use for the efficiency. But I have no hard data to back this up, it's just my expectation.
we also have this question: https://aviation.stackexchange.com/q/3777/1467 where it is said that "conventional" TR deflects both cold and hot streams

Yes, hot section thrust reversers are common on low-bypass turbofans and turbojets for both civilian and military applications.  Examples right off the top of my head are B727, early B737s, Panavia Tornado, Concorde,

Yes.
The Rolls-Royce/Snecma Olympus 593 [Wikipedia] were pure turbojets and they had thrust reversers.

Source: Wikimedia
Also, T/R on Concorde were also used in flight (If I remember correctly, only the inboard ones were used in flight) because Concorde didn't have spoilers.
Being a civilian aircraft, with the engines mounted under the wing, Concorde didn't have any real problem with thrust reversers

the last image shows some amount of cold air, though (the intake below the compressor)

@Federico, well, this is still a turbojet as there is not a "bypass" by the definition of bypass used in a turbofan. It's a cold flow of air used for cooling, but as it doesn't provide thrust I don't think we should consider it as a bypass flow. :-)

I accept your point, simply in my opinion is not strictly satisfying the requirement of the question (with no "cold" bypass flow), but I'll leave the final word to @mins.

@Federico: I'd accept this relatively small amount or ram air, which is not pre-compressed, and likely also hot due to the heat exchange. Besides I wonder if this air can continue to circulate when the reverser is deployed.

And, if you want a turbojet without any air flowing through the engine around the core, the 707-120 and DC-8-10 used Pratt & Whitney JT3C turbojets with thrust reversers.
Slightly-later models (the 707-220/-320 and DC-8-20/-30) used P&W JT4A turbojets, also with thrust reversers.
Over in Europe, the Caravelle VI-R used Rolls-Royce Avon 533R/535R turbojets with thrust reversers (the R in the designations of both the aircraft and the engine refers to their capability for Reverse thrust).


text:
How does the slotted flap work?
Slotted flap is an improved version of the plain flap, generating more lift (a fact I don't challenge). However the principle is air passing between the wing and the flap.

Source
This seems counterproductive as this airstream could also prevent the upper stream to follow the airfoils shape, and lead to air being less rotated downward than with a plain flap.
How does the slotted flap happen to be superior?

Related: What are the aerodynamic differences between the different types of slotted flaps?

The slotted flap re-energizes the boundary layer, preventing separation bubbles to appear. See What is the effect of airflow speed on separation?

The slot helps to prevent early separation, so the flap stays effective for larger deflection angles. What that means in reality can be read in this old NACA report which compares two NACA23012 sections, one with a plain flap and the other with a slotted flap. I have copied the pressure distributions below from that PDF:

Now I need to explain a little how to read the pressure distribution plots. The solid line shows the local pressure on the upper surface while the dashed line shows the pressure on the lower surface of the airfoil. The X-axis runs along the chord. The Y-axis represents pressure (suction is up) and y=0 represents ambient pressure. The area between the dashed and the solid lines is proportional to the lift coefficient, which is helpfully shown below each plot.
Now to the curvature: As long as the lines show a gradient, flow is attached. Separated flow can be recognized by a horizontal line slightly above the X-axis. As you can see, we have already fully separated flow on the upper plain flap surface at 30° flap angle and 8° angle of attack. At the same angles the slotted flap still shows fully attached flow on both surfaces. Attached flow creates a suction peak at the nose of the flap, which in turn allows a higher suction value at the end of the fixed part of the airfoil. This in turn allows a much higher suction peak at the nose of the airfoil, so that the suction force over the whole chord of the airfoil with the slotted flap is much higher than on the airfoil with the plain flap.
Only at 50° flap deflection will the slotted flap also show flow separation over the rear part of the flap, but there is still a suction peak which helps to stabilize the flow over the fixed part and increases lift. Unfortunately, the plain flap was not measured at the same angle, but from the small change between the 30° and 45° flap angles you can see already that moving the flap to 50° will change little.
The reason for this difference is simple: While the plain flap has only the old, thick and tired boundary layer coming from the fixed part of the airfoil to work with, the slot allows the slotted flap to create a new, thin and vigorous boundary layer which can tolerate much higher pressure gradients. Another benefit is the unchanging direction of the local flow behind the fixed airfoil: This allows to use a thin, highly cambered flap airfoil which maximizes lift production. The old NACA airfoil did not take advantage of this, but modern airliner flaps certainly do.

Nice explanation.New thin boundary layer is decelerate in slot,because slot represent contraction for flow,that is reason why slat decrease suction peak at leading edge at downstream element.isnt it?

@LostincurvedSpace-Time The forward element directs flow, so the AoA felt by the downstream element is lower. This is what diminishes the suction peak.

The answer lays into the pressure gradient.
The air that flows along the top surface comes from an area of (extreme) low pressure and has to travel down the wing, a direction where the gradient is "adverse": the pressure is increasing and the air would like to stop. The higher the lift being produced by the same wing, the higher this adverse gradient is.
When do we use flaps? When we need lots of lift at low speeds: it is a situation where the upper flow of air has the least incentive in remaining attached to the wing. The flow is slow and the gradient is as strong as it gets.
Enter the picture the cross flow of air passing through the slot. This is a flow coming from a high pressure region. It will encounter a low pressure region at the beginning of the flap surface, yes, but the remaining gradient will be completely negligible, and the flow will remain attached to the wing for longer, making a stall less likely.

Thanks Federico. "but the remaining gradient will be completely negligible": Do you mean the slot air will add speed to the up boundary layer, and (maybe by Bernoulli's principle) decrease its pressure, making it better sticking to the top face of the airfoil?

@ymb1, the 4 words following: "the pressure is increasing".

@mins I mean that the remaining difference in pressure, over the remaining length determine a gradient that is negligible for that flow.

Good article how any slot works.
Popular misconception is that air increase velocity in slot,this is not case.Same apply for slotted flap.
(A.M.O. Smith High lift aerodynamics),
page 518, chapter 5.3 Multi element Airfoils-General
quote from text:
"There are two things wrong with these statements.First of all,the slat does not give the air in the slot higher velocity.If anything,it gives the air low velocity."
https://charles-oneill.com/aem614/ReferenceMaterial/A+M+O+Smith+HIGH+LIFT+AERODYNAMICS.pdf

Slat effect—in the vicinity of the leading edge of a downstream element, the velocities due to circulation on a forward
element, for example, a slat, run counter to the velocities on
the downstream element and so reduce pressure peaks on the
downstream element.

Circulation effect—in turn, the downstream element
causes the trailing edge of the adjacent upstream element to be
in a region of high velocity that is inclined to the mean line at
the rear of the forward element. Such flow inclination induces
considerably greater circulation on the forward element

Dumping effect—because the trailing edge of a forward
element is in a region of velocity appreciably higher than
freestream, the boundary layer /'dumps" at a high velocity.
The higher discharge velocity relieves the pressure rise impressed on the boundary layer, thus alleviating separation
problems or permitting increased lift.

Off-the-surface pressure recovery—the boundary layer
from forward elements is dumped at velocities appreciably
higher than freestream. The final deceleration to freestream
velocity is done in an efficient manner. The deceleration of
the wake occurs out of contact with a wall. Such a method is
more effective than the best possible deceleration in contact
with a wall.

Fresh-boundary-layer effect—each new element starts
out with a fresh boundary layer at its leading edge. Thin
boundary layers can withstand stronger adverse gradients
than thick ones.


text:
What are these large yellow circles painted across the runway?
There are not many yellow markings on a runway. This row of six is painted about 400m from the threshold at both ends:

Montgomery Airport (Alabama) - Source: Google Maps
What does it mean for a pilot? Why yellow?

I count... six.

No, six. Runway markings are symmetrical about the centreline.

@mins It doesn't show on Google maps because they don't keep it strung all the time, only when they use the runway for arresting operations, and I'm guessing they close it to non-military traffic when they are doing it. I wouldn't want to hit that wire in a 172.

A large number of airports in the world are used for both civil and military operations and quite a few of these have arresting systems installed on them. According to Boeing Aero No. 13:

Of the nearly 36,000 airports around the world that are classified as civil, military, or joint-use, approximately 3,800 are used for scheduled commercial service. Worldwide, an estimated 2,000 aircraft arresting systems are installed at facilities in 64 countries.

The installation criteria for cable systems on commercial runways are identified in the U.S. Federal Aviation Administration (FAA) Advisory Circular AC 150/5220-9, Aircraft Arresting Systems for Joint Civil/Military Airports.
The location of the cable is marked on the runway by a series of reflective discs 10 ft (3 m) in diameter painted "identification yellow." These discs are laid out with 30 ft (9.1 m) between centers and extend the full width of the runway.

The location of a permanent aircraft arresting system that crosses operational runway pavement will be identified by a series of reflective circles 10 feet (3.05 meters) in diameter and painted solid yellow (striated marking will not be allowed) on the runway.  The circles will be 15 feet (4.57 meters) apart from edge to edge and extend the full width of the runway.  The middle two circles will straddle the runway centerline.

Arresting System Runway Pavement Marking, from FAA Advisory Circular 150/5220-9
The distance from threshold indicates whether most of the operations are conducted under visual or instrument meteorological conditions.

Image from Boeing Aero No. 13

When the cable is in place, it is at some distance from the surface. What happens to the civil aircraft rolling on it at high speed? That could also be a problem for the military ones as well, those that don't use it for landing, and for all aircraft when taking off.

@mins The cables are usually held by 6" rubber donuts- so they're about 3" above the surface; the main problem is for the aircraft nosegear- especially ones with FOD deflectors, which may get snagged on the cables. If required, the cables may be made to lie flat on the runway. Another important thing is that the cables are always held under tension so as to minimize any such incidents. One more way is to use only the runway without the cables; however, this reduces the available length for to/landing.

That would be the "line" telling military pilots where the arresting cables are. If you look to the side of those circles, you can see the arresting mechanism these. It would be yellow so that it would still stand out to the pilot and not be confused with the white runway markings.
You can find more about them here.

What are they used for? Practicing for landings on carriers?

@gsnedders These things


text:
Navier-Stoke vs Prandtl lift calculation
Why Prandtl had need to calculte lift with his lifting line theory (1933) if Navier-Stoke published equation long time ago 1822?
Also Navier-Stokes option is far more "accurate" then lifting line,N-S  are basics of CFD...

Because there were no computers in 1933?

@JanHudec,yes you are right,nevier -stokes is to big to solve by hands..

The Navier-Stokes equations represent a highly non-linear set of equations. Actually, although the have almost 2 centuries, they are one of the Millennium Prize Problems. Most of the interesting phenomenas represented by these equations include turbulence.
In specific conditions and hypothesis, analytical solutions have been demonstrated which is allowing us to understand the problem and physicis by reducing the complexity of the equations.
The law of Poiseuille appeared also after Navier-Stokes, and event the Darcy equation is empirical, not derived from Navier Stokes.
The interest of aerodynamics started to increase at the end of sXIX (first wind tunnel was constructed on 1871), so, in front of the complexity of this phenomena and the challenge the Navier-Stokes equations are some simplified equations appeared with some specific conditions. One of them was the the Prandtl lifting line theory.
One of the advantages of this theory is that relates the aerdoynamic properties of a wing to its geometry, without the need to calculate the complete flow field... think about that in CFD you have to calculate the complete flow field during hours (days?) in order to understand the properties and behaviour of a surface, this theory gives an analytical answer...
Still this theory is useful today, as helps to understand the behaviour of the wing.


text:
What are RVP signs?
I never saw these in the US, but certainly at UK airports and airfields you will often see "RVP" on a green background with a yellow border:

Source: http://www.sabre-roads.org.uk/gallery/displayimage.php?pos=-4476
What is the purpose of these signs, and who/what is their intended audience?

It's a Rendezvous Point for emergency vehicles. This is from the UK's Aerodrome Model Emergency Orders (appendix B, section 1.1.1):

Rendezvous Point signs should be displayed at the point(s) designated
  by the Aerodrome Emergency Orders as the rendezvous point(s) for all
  responding Emergency Services. Signs should be clearly visible from
  any direction from which responding Emergency Service vehicles/
  personnel are likely to approach when attending aircraft
  accidents/incidents within the response area defined by or cross-
  referenced in the Aerodrome Manual.


text:
Have other designs for individual gasper ventilation been tried?
The air gaspers (in large passenger aircraft) above the passengers' heads are fed from the main air conditioning system, at least in all aircraft that I am familiar with (see also this answer). This design probably makes sense, as it's very simple (no moving parts other than the gaspers) and takes advantage of a system which is already installed in the aircraft to provide additional functionality.
Still, I'm curious:

have other designs for individually adjustable passenger ventilation been tried (i.e. installed in large passenger aircraft), and why were they abandoned in favour of the current design? Off the top of my head I can think of a system with little fans above each seat - although it's probably far more prone to breaking than the current system.
Some cars have individual climate control (where the air supplied to each occupant can have a different temperature), has that ever been tried on a large commercial aircraft?

That doesn't seem related to aviation, the same question would apply as well to caoches, trains, etc.

@mins: I'm specifically interested in applications in aviation (specifically large commercial passenger aircraft), as the design challenges are unique (compared to cars, coaches, buildings...).

A bus or car has different requirements than an airplane @mins, plus even if it was the same it still relates to airplanes. I don't see why this is off-topic.

I think it's a valid question. I can also see why, if other systems have been tried, they've gone back to this - it's dead simple. One or two large fans push centrally cooled air down a couple of pipes above the pax cabin. Each individual aims and opens/closes a passive device to adjust how much of that airflow he gets. No other active devices to test, fail and replace. It's also rather light in comparison to individual fans, heating & AC equipment for each seat.

@FreeMan: I'm curious to see the significant differences in design, so far what is described seems to be very similar to this.

Whether or not they have been "tried" is probably not answerable, as "try this" type designs typically don't make it into production aircraft.
Look at the simplicity of the existing system, its simply some lightweight ducting with an adjustable air vent above each seat. The entire system has no other electric or adjustable parts, so maintenance is pretty easy, as well as reliability. Its also probably a hell of a lot easier to get certified.
Putting little fans above each seat wouldn't have any benefit here, as the air they move from one side of the fan to the other side has to be of a significant volume anyway, so you would still need ducting. The fan speed would be controllable, but then again so is the orifice size of the existing vents, so really no benefit there other than complexity and more wiring/electronics.
The existing system also works relatively well for individual climate control. Unlike in your car, you don't have a large space between you and the person next to you, so getting "individual" control is difficult (Seat A at X degrees, Seat B at Y degrees, etc). But note that even in your car you really aren't adjusting the heat or cold temperature, but the fan speed either through the AC system or through the heater. The heater and AC are at a constant temperature all the time.

I've seen cars (mid-range European cars) which have individual temperature controls for the driver and front passenger. To be honest I'm not entirely sure how they work or how effective they are, but that's what I was referring to.

@Lightsider - see the image link in mins' comment. They have the individual HVAC controls in many American cars, as well, and they work pretty well. I think the difference, as noted in comments and this answer, is that the weight and complexity of the gasper just can't be beat for the small benefit of a more complex set up when considering aviation needs.


text:
Which connector and cables are recommended for CAN?
Which mechanical connector(s) and cable(s) is/are recommended to arrange a Controller Area Network (CAN) bus communication or its aerospace counterpart ARINC 826 in the aerospace industry (civil & military)?

Aren't there specs defining the CAN bus and don't they include that information?

@FreeMan Yes to the former, no to the latter. The connectors are up to the implementer to define according to bus spec. I've seen CAN bus connectors that are everything from simple wire terminals through more complicated multi-function circular connectors.

@Ron Beyer: Exactly! This where my question pops from.

Well, silly me, @RonBeyer! I guess I'm much more used to the PC world where standards comprise both physical and electrical specifications. A circular shaped "USB" port is not USB because a round connector is not in the USB spec.

@FreeMan Not technically, no, but would it surprise you that in the industrial world, I see circular USB ports regularly? Even Ethernet quite often comes in M12, and serial connections are even worse.

@RonBeyer head asplode...

D-Sub and Mil Circular are pretty common with the LRUs I work with, but I haven't worked with anything CAN related, just ARINC 429, RS232/422/485

My avionics courseware shows ethernet is quite common, although having never maintained aircraft with a CAN bus, I don't have an opinion as to whether this is a good idea or not. I'm a 1553  and rs232/422 guy